Under jsx: preserve, actually preserve expressions which contain only comments #41757
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typescript-bot
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weswigham
commented
Dec 1, 2020
src/compiler/emitter.ts
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| @@ -3378,8 +3379,8 @@ namespace ts { | |||
| } | |||
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| function emitJsxExpression(node: JsxExpression) { | |||
| if (node.expression) { | |||
| writePunctuation("{"); | |||
| if (node.expression || (!commentsDisabled && !nodeIsSynthesized(node) && getTextOfNode(node).length > 2 && getTextOfNode(node).indexOf("/*") > -1)) { // preserve empty expressions if they contain comments! | |||
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hasCommentAtPosition isn't a thing we currently have, but this does a, okay job of approximating it. Obviously doesn't handle something like
const x = <div>
{ // first line
/*last line*/}
</div>;Maybe it's worth doing a full check with forEachTrailingCommentRange? @rbuckton - your opinion?
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do we care about // comments? The new check only handles /**/ comments, right?
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Yep. That's why I'm asking if it's worth doing a full comment range iteration to check if there are any comments attached to the position.
weswigham
commented
Dec 1, 2020
| @@ -1790,7 +1790,7 @@ namespace ts { | |||
| const name = importDeclaration.propertyName || importDeclaration.name; | |||
| return setTextRange( | |||
| factory.createPropertyAccessExpression( | |||
| factory.getGeneratedNameForNode(importDeclaration.parent.parent.parent), | |||
| factory.getGeneratedNameForNode(importDeclaration.parent?.parent?.parent || importDeclaration), | |||
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This change (and the similar ones in system) are what fix the crash mentioned in the OP. The non-module file has a reference to a synthetic import that, since it's never actually inserted into the file (since it's not a module), is never parented, and thus has no name. We emit a (admittedly type system, rather than grammar/program) error in these cases usually (module "react/jsx-runtime" not found), so the emitted JS being nonfunctional is probably fine, but this case might need a more descriptive error added. The emit simply uses an arbitrary name now (_a), rather than crashing.
Since this part fixes a crash, I'm wondering if I should (partially?) port this to the 4.1 branch or no? @DanielRosenwasser ?
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This comment may actually be referring to the crash fixed here (assuming the input file is exactly what the user in that comment says, odd as a top-level return is, since we wouldn't mark that as a module), though the stack is very different than the on the OP of that thread refers to (and is definitely a separate issue).
sandersn
requested changes
Dec 2, 2020
tests/baselines/reference/commentsOnJSXExpressionsArePreserved(jsx=preserve,module=commonjs).js
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src/compiler/emitter.ts
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| @@ -3378,8 +3379,8 @@ namespace ts { | |||
| } | |||
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|
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| function emitJsxExpression(node: JsxExpression) { | |||
| if (node.expression) { | |||
| writePunctuation("{"); | |||
| if (node.expression || (!commentsDisabled && !nodeIsSynthesized(node) && getTextOfNode(node).length > 2 && getTextOfNode(node).indexOf("/*") > -1)) { // preserve empty expressions if they contain comments! | |||
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do we care about // comments? The new check only handles /**/ comments, right?
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@sandersn since nobody else weighed in, I opted to change this to do a full comment scan. It's ready for another look. @typescript-bot perf test this - this hopefully doesn't hurt |
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Heya @weswigham, I've started to run the perf test suite on this PR at d1db247. You can monitor the build here. Update: The results are in! |
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@weswigham Here they are:Comparison Report - master..41757
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Eyyy, and we don't have emit on for |
sandersn
approved these changes
Dec 18, 2020
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And, perhaps more importantly, fixes a crash caused by the interaction of the
moduleorsystemtransformers and the newjsxtransforms discovered along the way (in the same test case).Fixes #41754